The correct adjustment of the tire pressure in the tires of motor vehicle wheels is especially important in many respects. On the one hand, excessively high or low air pressure leads to elevated wear of the tires so that the vehicle tires must be replaced prematurely. This involves high costs. On the other hand, in the case of excessively low air pressure in the vehicle tires, tire life may be impacted because the tires, especially the sides of the tires, are subjected to increased flexing. Excessive flexing in this case leads to excessive heating in the interior of the tire and therefore affects the sidewall of the tire. This also results in a decrease in the strength of the tire, which may lead to a flat tire. The user of the vehicle must therefore regularly check the air pressure of the vehicle tires and correct it if necessary. However, this is frequently neglected for various reasons. Therefore, tire air pressure monitoring systems have been developed in which each vehicle tire is assigned an air pressure monitoring device which automatically measures the air pressure in the vehicle tire and reports a deviation from the nominal pressure to the driver of the vehicle via a suitable control unit. Such air pressure monitoring devices, for example, can be arranged in the tire in question, vulcanized into the rubber, or adhered or arranged in the air valve of the tire or in the rim.
For example, from EP 0 391 922 B1 it is known that a tire pressure sensor can be provided for vehicles with a pressure switch actuated by the tire pressure and attached to the periphery of the rim of the vehicle radially to the wheel axle. A short distance from it in the region of the tire pressure sensor on the wheel suspension of the vehicle a signal pickup is mounted which senses high frequency vibration in the tire pressure sensor when it passes by the vehicle wheel upon each rotation. The signal pickup is connected to an evaluation circuit with a warning indicator connected to it which emits a warning signal in the case of low pressure in a tire.
The disadvantage here is that a signal pickup such as a detector mounted in the region of the vehicle suspension is always exposed to dirt and moisture. Furthermore, in the region of the wheel suspension, the metal construction parts may have a disturbing influence on the high frequency vibrations between the tire pressure sensor and the signal pickup and transmit incorrect measured values of the tire pressure.
From DE 196 18 658 A1, for example, an air pressure control system for vehicles is known in which each vehicle tire is assigned an air pressure monitor installed, for example, in the tire rubber or in the valve. These devices have a transmitter which transmits the data to a corresponding receiver in a contactless manner. A central unit evaluates the data from the air pressure monitor together with data from additional sensors measuring the wheel rpm and generates a warning signal for the vehicle driver when the pressure falls below a certain minimum. The receiver in this case is arranged in a place in the vehicle not shown in detail. The disadvantage in this case is that only warning notifications or warning signals representing all vehicle tires together are emitted.